Femtosecond two-photon LIF imaging of atomic species using a frequency-quadrupled Ti:sapphire laser
Femtosecond two-photon LIF imaging of atomic species using a frequency-quadrupled Ti:sapphire laser
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DOI：
10.1007/s00340-014-5845-7
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发表时间：
2014-04
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影响因子：
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通讯作者：
W. Kulatilaka;J. Gord;Sukesh Roy
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文献类型：
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作者：
W. Kulatilaka;J. Gord;Sukesh Roy
飞秒（fs）持续时间的激光脉冲非常适合于双光子激光诱导荧光（TPLIF）成像的关键原子物种，如H，N和O的气相反应流。超短脉冲能够实现有效的非线性激发，同时减少干扰光化学过程。此外，放大的fs激光器能够实现高重复率成像（通常为1-10 kHz），以捕获湍流场的动态特性。然而，二维（2D），单激光拍摄的fs-TPLIF成像的上述物种是具有挑战性的，在大多数实际的流场，因为有限的紫外脉冲能量可在商业光学参量放大器（OPA）为基础的可调谐激光源。在这项工作中，我们报告了一个有效的，fs四倍频单元的发展[即，四次谐波发生器（FHG）]的总转换效率比基于OPA的商用系统高六倍以上。详细介绍了用于火焰中H原子二维成像的fs-FHG系统的发展、特性和应用。讨论了同一激光系统在氮原子和氧原子二维成像中的潜在应用。
Femtosecond (fs)-duration laser pulses are well suited for two-photon laser-induced-fluorescence (TPLIF) imaging of key atomic species such as H, N, and O in gas-phase reacting flows. Ultrashort pulses enable efficient nonlinear excitation, while reducing interfering photochemical processes. Furthermore, amplified fs lasers enable high-repetition-rate imaging (typically 1–10 kHz) for capturing the dynamics of turbulent flow fields. However, two-dimensional (2D), single-laser-shot fs-TPLIF imaging of the above species is challenging in most practical flow fields because of the limited ultraviolet pulse energy available in commercial optical parametric amplifier (OPA)-based tunable laser sources. In this work, we report the development of an efficient, fs frequency-quadrupling unit [i.e., fourth-harmonic generator (FHG)] with overall conversion efficiency more than six times greater than that of commercial OPA-based systems. The development, characterization, and application of the fs-FHG system for 2D imaging of H atoms in flames are described in detail. The potential application of the same laser system for 2D imaging of N and O atoms is also discussed.